Peroxydicarbonates of the formula R--OCO--OO--OCO--R, wherein R is an organic radical derived from monohydric alcohols of the type ROH, are widely used as initiators in the polymerization of unsaturated monomers as described, for example, in U.S. Pat. No. 2,464,062.
The peroxydicarbonates are typically prepared by the so-called "peroxide slurry method" wherein a chloroformate of the formula R--OCO--Cl (wherein R is as above defined) is reacted with a concentrated aqueous slurry of sodium peroxide as described, for example, in U.S. Pat. No. 2,370,588.
It has been found, however, that during the addition of the sodium peroxide slurry to the reaction mixture, the reaction product tends to hydrolyze to form the corresponding alcohol resulting in an impure product having a reduced peroxydicarbonate assay. In addition, hydrolysis of the reaction product reduces the net yield of peroxydicarbonate.
Since the lower molecular weight alcohols, for example, ethanol, isopropanol, n-propanol, t-butanol, sec-butanol, and the like are relatively water soluble, such lower molecular weight alcoholic impurities can be readily removed from the peroxydicarbonate by washing with water. However, since the water solubility of alcohols generally decreases with increasing molecular weight, the higher molecular weight alcoholic impurities such as, for example, 2-ethylhexanol, are not readily removed from the peroxydicarbonate by typical product purification means, e.g., water washing.
Regardless of the ease of removal of the alcoholic impurity formed by hydrolysis of the reaction product upon addition of the sodium peroxide slurry, the yield of peroxydicarbonate is reduced in proportion to the extent of hydrolysis.
Published German Patent application No. 1,443,840 discloses adding sodium hydroxide to a colloidal dispersion of hydrogen peroxide and chloroformate, which entails the use of costly, complex equipment. Moreover, the process described in said German application requires the addition of a perhalogenated solvent before, during or at the completion of the reaction, with the consequence that only dilute solvent solutions of peroxydicarbonate are obtained. Although the German application states that peroxydicarbonate can be recovered from the solvent solution by distillation, this requires an additional costly and time consuming processing step which is potentially hazardous.